1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
The coverage area of a wireless communication system is typically divided into a number of geographic areas that are conventionally referred to as cells. Each cell is associated with a base station (or access network) that provides wireless connectivity to the cell. Mobile units located in the coverage area of a cell may access the wireless communications system by establishing a wireless communication link, often referred to as an air interface, with one or more base stations. The air interface typically supports a variety of channels including dedicated channels, control channels, access channels, and the like. Dedicated (traffic) channels are logical channels allocated to an individual mobile unit for the exchange of data and/or voice signals. Control channels are common downlink (or forward link) channels used to provide information to mobile units, e.g., to alert mobile units that there is a call or data waiting for the mobile unit.
Access channels are common uplink (or reverse link) channels used for short signaling message exchanges such as call originations, responses to pages, and registrations. For example, in wireless systems such as Code Division Multiple Access (CDMA2000), Evolution Data Optimized (EVDO), Evolution Data and Voice (EVDV) and Universal Mobile Telecommunication System (UMTS), a random access channel is used by the mobile units to communicate with the access network when there is no dedicated channel assigned. A set of access channel parameters is used to control how messages are transmitted over the access channel. Some access channel parameters may be broadcast to mobile units over a common control channel. However, in that case all of the mobile units will transmit messages over the access channel according to the same broadcast access channel parameters. Some access channel parameters may also be negotiated between individual mobile units and the wireless communication system. However, these negotiations require message exchanges over either the common channel or a dedicated traffic channel between the mobile unit and the wireless communication system. Access channel parameter negotiations are both time-consuming and resource-consuming.
The wireless communication system is not typically capable of controlling access channel transmissions by the mobile unit. For example, mobile units may randomly originate and transmit messages over the access channel according to the predetermined or previously negotiated access channel parameters. For another example, multiple page messages sent on a common control (or paging or broadcast) channel may be received by multiple mobile units at approximately the same time. These page messages may therefore trigger multiple response messages from multiple mobile units that may be transmitted over the access channel according to the predetermined or previously negotiated access channel parameters. At least in part because the mobile units may be using the same access channel parameters, the response messages may be sent in the same slot on the access channel, thereby causing a collision. In the current standards, colliding response messages back off randomly and are then retransmitted at a higher power. Thus, collisions between response messages typically incur large resource costs and long delays, which may degrade performance of the wireless communication system.